sink

to displace part of the volume of a supporting substance or object and become totally or partially submerged or enveloped; fall or descend into or below the surface or to the bottom (often followed by in or into):

The battleship sank within two hours. His foot sank in the mud. Her head sinks into the pillows.

2.

to fall, drop, or descend gradually to a lower level:

The river sank two feet during the dry spell.

3.

to settle or fall gradually, as a heavy structure:

The tower is slowly sinking.

4.

to fall or collapse slowly from weakness, fatigue, distress, etc.:

He gasped and sank to his knees.

5.

to slope downward; dip:

The field sinks toward the highway.

6.

to go down toward or below the horizon:

the sun sinks in the west.

7.

to penetrate, permeate, or seep (usually followed by in or into):

Wipe the oil off before it sinks into the wood.

8.

to become engulfed or absorbed in or gradually to enter a state (usually followed by in or into):

to sink into slumber.

9.

to be or become deeply absorbed or involved in a mood or mental state (usually followed by in or into):

sunk in thought. She sank into despair.

10.

to pass or fall into some lower state, as of fortune, estimation, etc.; degenerate:

to sink into poverty.

11.

to decline or deteriorate in quality or worth.

12.

to fail in physical strength or health.

13.

to decrease in amount, extent, intensity, etc.:

The temperature sank to 30° at noon.

14.

to become lower in volume, tone, or pitch:

Her voice sank to a whisper.

15.

to enter or permeate the mind; become known or understood (usually followed by in or into):

The transitive use (mid-13c.) supplanted Middle English sench (cf. drink/drench) which died out 14c. Related: Sank; sunk; sinking. Sinking fund is from 1724. Adjective phrase sink or swim is from 1660s. To sink without a trace is World War I military jargon, translating German spurlos versenkt.

sink

n.

early 15c., "cesspool, pit for reception of wastewater or sewage," from sink (v.). Figurative sense of "place where corruption and vice abound" is from 1520s. Meaning "drain for carrying water to a sink" is from late 15c. Sense of "shallow basin (especially in a kitchen) with a drainpipe for carrying off dirty water" first recorded 1560s. In science and technical use, "place where heat or other energy is removed from a system" (opposite of source), from 1855.

A part of the physical environment, or more generally any physical system, that absorbs some form of matter or energy. For example, a forest acts as a sink for carbon dioxide because it absorbs more of the gas in photosynthesis than it releases in respiration. Coral reefs are a long-lasting sink for carbon, which they sequester in their skeletons in the form of calcium carbonate.